1. Field of the Invention
The present invention relates to processes for producing exhaust gas manifolds that have a flange for fastening to the cylinder head of an internal combustion engine, manifold pipes for leading off the exhaust gases flowing out from the cylinders, and a pipe connector, wherein the pipe connector has openings for the manifold pipes.
2. Description of the Background Art
Exhaust gas manifolds typically include a flange, which is fastened to the cylinder head of an internal combustion engine, and a number of manifold pipes corresponding to the number of cylinder outlets for leading off the exhaust gases flowing out from the cylinders. The ends of the manifold pipes are brought together, so that all exhaust gases pass through further components of the exhaust system, e.g., catalysts, diesel soot filters, and mufflers. For this purpose, the ends of the manifold pipes, depending on the engine design, are designed as 3-into-1, 4-into-1 or 4-into-2-into-1 connectors.
DE 94 17 043 U discloses the bringing together of 4 manifold pipes. For this purpose, the pipe ends are deformed such that they form the 4 quadrants of a circle. As soon as the gap between the pipe ends is welded together gas-tight, the combination is complete.
In practice it has been found that because of tolerances in the pipe dimensions themselves or because of tolerances that occur during the forming of the pipes and the pipe ends, gaps form, which can only be closed by additional welding work. This is disadvantageous.
Additional drawbacks of the welding process are weld spatters, which break off later during operation of the exhaust system and can destroy mechanically sensitive components of the exhaust system, especially ceramic monoliths and soot filters. Also problematic are contaminations that can occur during welding. This leads to the fact that the welded exhaust manifolds must be washed and cleaned, which considerably increases the production costs. This is extremely unsatisfactory.
Naturally, there has been no lack of attempts to eliminate these problems by changing the design. For example, U.S. Pat. No. 4,833,882 shows a pipe connector for manifold pipes, formed by a massive casting, which has a separate connection port for each manifold pipe end. In addition, a connection port for a lambda probe is provided. The connection to the subsequent pipes is provided by a massive flange plate. Although the tolerance problem is somewhat reduced by this, the problems associated with welding remain. In addition, there is the relatively high weight.